How to remove the default e-mail signature on the Kindle Fire
Does the world really need to know that you sent an e-mail from your Kindle Fire? We'll show you how to remove the default signature.
Mobile device manufacturers still seem to think that adding a default signature, letting the world know what device you sent an e-mail from, is a good idea.
By default, the e-mail client on the Kindle Fire adds "Sent from my Kindle Fire" at the end of all messages you send. Here's how to remove it:
Step 1: From the inbox of your Kindle Fire, go to Settings.
Step 2: Under the "Sending mail" section, select Composition defaults.
Step 3: Remove or edit the signature from the text box. If you prefer to turn off signatures, uncheck the Use Signature box.
That's it. If you're considering keeping the signature, read Al Sacco's post at CIO.com on why you shouldn't.

